Conventionally, portable terminals, which have high usability while reducing the height of their operation keys, have been known in the field of portable terminals for which portability is of great importance.
For example, Japanese Published Patent Application No. H11-329149 describes a portable terminal having key switches that are operated by pressing the tops thereof, in which key base portions of the key switches are made of a resin film sheet having a uniform thickness.
Moreover, Japanese Published Patent Application No. 2003-281965 describes a portable terminal device having operation buttons, in which each operation button is formed by a key made of a resin, a stroke member made of an elastic material and provided immediately under the key, and a key switch having a contact that is depressed through the stroke member when the key is depressed, and an electrode on a substrate which is contacted by the contact.
Moreover, Japanese Published Patent Application No. 2006-66157 discloses a key input device structure of portable communication devices, in which a key sheet having a plurality of key buttons formed thereon, and a printed board are mounted in a housing having an upper case and a lower case, and openings are formed in the upper case so as to expose operation portions of the plurality of key buttons. In this key input device structure, restricting members for restricting positional displacement of the key sheet relative to the openings are formed so as to protrude from fixed locations near the key sheet toward the key sheet.